The clashes erupted before dawn when dozens of Islamic State militants attacked the military bases after heavy mortar barrage and machine gun fire in Zuwiyah area, about 250 kilometre north of here, a source told Xinhua news agency.

Representational image. AP

The troops fought back and foiled the attackers from storming their bases, but the militants managed to block the main road between Salahuddin's province capital Tikrit and the city of Mosul in northern Iraq, the source said.

In the morning, reinforcement troops and helicopter gunships reopened the main road after defeating the extremist militant, who withdrew to Makhoul mountain range in the northern part of Tikrit, the source added.

After the withdrawal of the extremist militants, the troops found 12 of their bodies and two destroyed armoured vehicles, three trucks along with a large amount of weapons and ammunition left on the battlefield, the source said.

The clashes also resulted in the killing of three soldiers and the wounding of eight others, the source added.

Iraqi security forces and allied paramilitary Hashd Shaabi units freed Tikrit and other key cities and towns in the predominately Sunni Arab province of Salahudin from the extremist Islamic State group in June 2014.

The incident came as Iraqi prime minister Haider al-Abadi declared Mosul's liberation on 10 July after nearly nine months of fierce fighting to dislodge the extremist militants from their last major stronghold in Iraq.